<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
   <link rel="stylesheet" href="./style/YS.css">
</head>
<body>
    <button class="btn">我是按钮</button>
    <script>
        document.querySelector('button').onclick = () =>{
            alert('你点我干嘛')
        }
    </script>
</body>
</html>